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Invited speaker presentation

A limited number of foods are responsible for the majority of reactions in IgE-mediated
food allergy, seafood, peanut and tree nut allergies predominating in adults whilst
cow’s milk and hen’s egg are important allergenic foods for infants. Over the past
10 years there has been an explosion in the numbers of well characterized allergens
which have been sequenced and collected into a number of databases which has facilitated
bioinformatic analyses and allowed food allergens to be classified according to their
structural and biological properties. This has shown that food allergens belong to
only a limited number of protein superfamilies, with animal and plant derived food
allergens showing similar distributions, the majority of allergens in each group falling
into just three to four families with a tail of between 14 to 23 families comprising
between 1-3 allergens each. Thus, around 65% of plant food allergens belong to just
four protein families, the prolamin, cupin, Bet v 1-like, and profilin families whilst
animal food allergens can be classified into three main families, the tropomyosins,
EF-hand proteins, and caseins.Such patterns of behavior beg the questions what makes
some foods such as peanut so much more allergenic than other closely related foods
such as pea? Why do certain protein scaffolds dominate the landscape of allergen structures?
Can we identify structural features that predispose certain proteins to becoming allergens?

That the relationship between protein structure and allergenicity is not straight
forward is indicated by the fact that previous detailed analysis of the secondary
structure elements in proteins has not shown any relationship with allergenicity.
It is further complicated by factors such as food processing and modification of allergen
structures during digestion. Only a small number of the total number of proteins expressed
in, for example an edible seed such as peanuts, have been defined as allergens and
abundance alone does not account for the allergenic potency of certain proteins. Another
factor that may be involved in determining allergenic potential of certain proteins
is their stability to conditions commonly used in processing foods, especially in
food such as peanuts which are rarely consumed raw. Lastly, in order for food proteins
to either sensitize or elicit an allergic reaction they must also be bioaccessible,
i.e. released from the food matrix and then survive gastrointestinal processing to
be presented to the mucosal immune system in an immunologically relevant form. Structural
therefore factors may contribute to the allergenicity of certain protein scaffolds
and may vary between different scaffolds. Future work will focus on how the food matrix
may modulate the bioaccessibility and digestion properties of these proteins and the
route by which specific proteins drive class switching in B cells. Only by combining
the knowledge and skills of allergen biochemists, immunologists and clinical allergists
will the step-changes in thinking be achieved to address these questions in future.

Acknowledgements

ENCM was supported by the UK Biological and Biotechnological Sciences Research Council
through a strategic program me grant to IFR.